If you change a formula in someone else’s file you should tell them. In fact there are a few things you should do to make it easier. This can apply to changes to your own files as well.

Things you should do

• change the colour of the cell(s) you changed (bright yellow works well)
• tell them you have made a change – either verbally or via email (don’t just make a change and not tell them) also let them know the colour you used to mark the cell(s)
• add a cell comment to the cell explaining why you changed it
• depending on the file there could be a change log that needs to be updated

Exceptions

This can apply to a cell formula that is an “exception” within its range.

There may be a valid reason for it to be different, so changing it’s colour and adding a cell comment can help stop it being accidentally copied over.

Having a different colour also brings people attention to it if there are queries.

I have been using spreadsheets long enough to know that exceptions exist and you have to be able to handle them.

Hiding changes is not the way to handle them!

Yes, protecting files can stop this, but most Excel files don’t have protection turned on.